1. Field of the Invention
In the above-method of combustion, the non-premixed fuel contains a combustible material and substantially free of an oxidizer. If the non-premixed fuel contains an oxidizer, the amount of the oxidizer is in an amount smaller than about 0.5% of the amount that is minimally required to completely oxidize the combustible material therein. The premixed fuel may be a mixture comprising an oxidizer and at least one combustible material. The non-premixed fuel comprises the at least one combustible material. The method may further comprise supplying an oxidizer through at least one nozzle into the chamber. The non-premixed fuel may be supplied into the combustion chamber through a plurality of nozzles.
2. Description of the Related Art
In general, flames used in gas fuels are broadly classified into a non-premixed flame (diffusion flame) in which air and fuel are separately supplied and a premixed flame in which air is beforehand mixed with fuel and the air/fuel mixture is supplied.
In non-premixed flames (diffusion flames), the range of stable flame conditions is wide but smoke is likely to be produced. In premixed flames, however, NOx emissions can be easily controlled but there is a risk of backfire or blowout. Since great importance has recently been attached to environmental pollution, emission characteristics of pollutants as well as flame stability have been considered major factors for the design and development of combustors.
As a method for reducing NOx emissions, a method for reducing combustion temperature through burnt gas recirculation, a method for performing multi-stage combustion and the like are well known in the art. The method for reducing combustion temperature through burnt gas recirculation has a problem in that it can reduce NOx emissions but requires additional design and devices for burnt gas recirculation. Further, the method for performing multi-stage combustion has been widely employed but still has a problem in that the relevant devices and their operation are complicated.
Recently, combustors tend to require high heating loads, compact size and light weight, and little environmental pollution emission. Thus, researchers and companies in combustion fields aim to develop a high efficiency, low pollution combustion technology and to put such technology to practical use.
In case of the high load combustion, combustion should be produced in a high-velocity flow field in which strong turbulence has occurred, but flames may either be extinguished due to high shear strain rates or become unstable due to abnormalities of combustion flow characteristics. Therefore, this may lead to more serious problems since more pollutants can be discharged and the combustion efficiency can also be reduced.
In particular, Japanese Patent Laid-open Publication No. (Hei) 7-103428 discloses a technology in which an oxygen nozzle for injecting oxygen-enriched air at high speed is installed in a central portion of a burner and fuels are injected through a plurality of nozzles installed on an outer concentric circle of the oxygen nozzle. In such a type of burner, combustion gas is introduced into a furnace as the air (oxygen) is injected at a high speed. Thus, the temperature of combustion gas in the vicinity of a burner outlet and the concentration of oxygen within the combustion air can be reduced so that the NOx emissions are reduced. Recently, this technology has been widely studied as a method for reducing NOx emissions due to high temperature combustion.
However, this technology has a problem in that it cannot be applied to practical use since its minimum NOx emission is 200 ppm or more. Furthermore, the methods for performing multi-stage combustion and the burnt gas recirculation as an existing method for reducing the NOx emissions have problems in that the production costs are high and workability and manufacturability are lowered due to the complex structures of relevant devices.